A device that detects and transmit the biological response into an electrical signal. It integrates a biological element with a physiochemical transducer to produce an electronic signal proportional to a single analyte which is then conveyed to a detector. It also determines the presence and concentration of a specific substance in any solution. According to IUPAC definition, "A biosensor is a self contained integrated device that is capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element which is in the direct spatial contact with a transduction element."

This device was invented by Professor Leland C Clark, who is known as the father of Biosensor. The work started in the year 1916 when the immobilization of proteins : adsorption of invertase on activated charcoal was reported. The first glass pH electrode came in 1922. Professor Clark published his definitive paper on the oxygen electrode in 1956. Then he mentioned an amperometric enzyme electrodre for glucose in 1962. In 1969, Guilbault and Montalvo discovered the first potentiometric biosensor: urease immobilized on an ammonia electrode to detect urea. An ion selective Field Effect Transistor (ISFET) came in 1970 and a fiber-optic sensor with immobilized indicator to measure carbon dioxide or oxygen was presented by Lubbers and Opitz in the year 1975. The year 1980 saw the invention of fiber optic pH sensor for in vivo blood gases. The first surface plasmon resonance (SPR), immunosensor came in 1983 and the first mediated amperometric biosensor came in 1984. The blood-glucose biosensor was launched by MediSense ExacTech in 1987.

The basic components of biosensor are Bioelement and Transducer.

Bio-element is a typically complex chemical system which is extracted or derived directly from an organism. These are generally, enzymes, antibodies, oxidase, tissues, polysaccharide and nucleic acid. Their main function is to interact specifically with a target compound i.e. the compound which is to be detected.

Transducer basically converts biological response into an electrical signal.

The workflow of the bio-sensor is as follows:
Bio-element--->Transducer--->Amplifier--->Processor--->Display
The complex substance derived from biological organism is the bioelement. Now, transducer converts this complex substance into electrical signal. This signal is amplified by the amplifier. The processor process these amplified signals and then it is displayed.

Characteristics of a biosensor:-
1. LINEARITY- the linearity of the biosensor should be high for the detection of high substrate concentration.
2. SENSITIVITY- the value of the electrode response per substrate concentration.
3. SELECTIVITY- the chemicals Interference must be minimised for obtaining the correct result.
4.RESPONSE TIME- the required time which is important for getting 95% of the response.

Some of the examples of biosensors are :
a) Pregnancy test- Biosensor helps in detecting the hCG protein in urine.
b) Glucose test for diabetic patients- the glucose level of the blood can be monitored by using a biosensor.

Technique of biosensor are - Fluorescence, DNA Microarray, SPR Surface plasmon resonance, Impedance spectroscopy, SPM (Scanning probe microscopy, AFM, STM), QCM (Quartz crystal microbalance), SERS (Surface Enhanced Raman Spectroscopy).

Types of biosensors are as follows:-
i) Calorimetric Biosensor- If the enzyme catalyzed reaction is exothermic in nature, then two thermistors are used to measure the difference in resistance
between the reactant and product and hence the analyte concentration are measured.

ii) Potentiometric Biosensor- For voltage change in distribution of charge is detected using ion-selective electrodes, such as pH-meters.

iii) Amperometric Biosensor- it measures the electric current. Based on oxidase enzymes that generate H2O2 and consume oxygen. Formation of H2O2 can be detected by the help of Platinum-electrode.

iv) Optical Biosensor- it measure the change in light adsorption.

v) Piezo-electric Biosensor- this device detects the specific angle at which electron waves are emitted when the substance is exposed to laser light or crystals, such as quartz, which vibrate under the influence of an electric field.

vi) DNA biosensor- the applications of clinical diagnosis and genome mutation detection helped in the manufacture of DNA biosensor. For e.g.- Electrodes, Chips and Crystals.

Different applications of biosensors are:-
Biosensors in process control will be able to measure materials in the process flow of temperature, pressure and the acidity readings.

In food industry, biosensors are used to analyse and monitor the freshness of food.

Potentiometric biosensors are intended primarily for monitoring levels of carbon dioxide, ammonia, and other gases dissolved in blood and other liquids.

Glucose monitoring in diabetic patients.

Analytical measurement of folic acid, biotin, vitamin B12 and pantothenic acid.

Enzyme-based biosensors are used for continuous monitoring of compounds such as methanol, acetonitrile, phenolics in process streams, effluents and groundwater.

Study of bio-molecules and their interaction.

Drug development and evaluation of biological activity of new compounds.

Forensic use.

Medical diagnosis-determination of drug residues in food, such as antibiotics and growth promoters. In the field of medicine, tumor cells are used as a biosensor to monitor chemotherapeutic drug susceptibilities.

Environmental field monitoring-the detection of pesticides and river water contaminants.

Quality control

Industrial Process Control- The development of biosensors in industry can improve manufacturing techniques, which would allow for a wider range of sensing molecules to be produced at a cheaper rate.

Detection systems for biological warfare agents

Manufacturing of pharmaceuticals and replacement organs- Biosensors also play a role in the manufacturing of pharmaceuticals and replacement organs such as an artificial pancreas for diabetics.

These applications represent the wide utility of biosensors which are cheap, small, and portable devices. It plays a part in the field of medicine, environmental quality, and industry mainly by identifying material and the degree of concentration present. They are advantageous in many prospects and can bring a huge change in our lifestyle.

About Author / Additional Info:
Geetanjali Murari
Email Id: geetanjali1232@gmail.com